/**
 * The parent class of state
 */
public class ShopState implements IShopState {
    public ShopState() {
    }

    public void shop() {
    }

    public void generateBill() {
    }

    public void pay() {
    }

    protected void changeState(ShopContext c, ShopState s) {
        c.changeState(s);
    }
}